You can also use
sudo apt-get install dconf-editor
After starting the
dconf-editor, navigate to org >> gnome >> desktop >> input-sources
Add the options that you need in
xkb-options. The option strings are surrounded by single quotes and separated by commas. Be careful not to delete the brackets on the ends.
To enable ctrl+alt+backspace to kill the X-session, add
You can use this method to enter most of the traditional xkb options that are no longer available in System Settings >> Text Entry. The exceptions are the settings for switching the keyboard layouts, which currently do not work because of a bug.
For a list of the options and the syntax, use
man 7 xkeyboard-config in a terminal.